Sgt. Bergdahl’s lawyer has argued that Mr. Trump has compromised his client’s right to a fair and impartial trial. Over the past several months, Mr. Trump has continually made statements at campaign events calling Sgt. Bergdahl a traitor and saying he “should have been executed.”

Now Sgt. Bergdahl’s lawyer is concerned that, due to Mr. Trump’s large media influence, potential jurors have already been poisoned against him, Bloomberg View reported.

If Mr. Trump is compelled to testify in the proceedings, he could be required to appear in the middle of the presidential election season.

The military courts may not be convinced that Mr. Trump’s influence over politics and public opinion are legally relevant to Sgt. Bergdahl’s constitutional right to receive a fair trial, but if the court grants his lawyers a motion to have a hearing on the issue, Mr. Trump could be called to the stand.

If Mr. Trump is called and refuses to attend, he could be subpoenaed, according to Bloomberg.

“The First Amendment rules out any effort to prevent Mr. Trump from making these defamatory remarks,” Mr. Bergdahl’s lawyers argued in a court filing. “The fact remains, however, that his pattern of doing so, with the full glare of public attention before mass audiences around the country, materially threatens Bergdahl’s right to fair consideration by the convening authority as well as in a court-martial.”

In December, Mr. Fidell blasted the GOP front-runner for spreading misinformation about the case and asked that Mr. Trump “cease his prejudicial monthslong campaign of defamation against our client.”

Mr. Fidell told The Associated Press in an interview that Mr. Trump has stated that five soldiers were killed trying to find Sgt. Bergdahl after he was captured by the Taliban. The Pentagon has said no one died in the search.

Mr. Trump has also pledged to review the case if Sgt. Bergdahl is not appropriately punished.

Mr. Trump is not the only figure Sgt. Bergdahl’s lawyers have criticized for publicly opining about the case. Last summer, Fidell argued in court that comments by the Senate Armed Services Committee chairman, John McCain, were having undue influence on the case because the Army officer presiding over the case was up for a promotion that required Senate confirmation.

Sgt. Bergdahl, who was held captive by the Taliban for five years after leaving his post, has been charged with misbehavior before the enemy and desertion. The first charge carries a potential life sentence. His court-martial is scheduled for August.